The long-term goal is to more precisely quantify many of the more than 46 parameters so far identified that affect the transmission dynamics of LaCrosse (LAC) virus and its maintenance in nature. It is hypothesized, using a deterministic model, that maintenance of a stable virus prevalence is 50 percent dependent on vertical (transovarial) transmission by the vector, Aedes triseriatus, 25 percent dependent on paternal horizontal amplification (venereal transmission by transovarially infected male Ae. triseriatus), and 25 percent dependent on horizontal amplification via vertebrates, i.e., chipmunks, tree squirrels, and foxes. Vertical factors to be studied include net replacement rate of transovarially infected females relative to uninfected females; paternal amplification factors include male mating behavior and venereal transmission efficiency. Vertebrate amplification factors to be studied include titre and duration of viremia in juvenile versus adult chipmunks, and survivorship of orally infected Ae. triseriatus females to the second post-infection oviposition (at which time they become vertical transmitters). An attempt will also be made to develop better field sampling methods for Ae. triseriatus. The studies should continue to lead toward a future capability for reducing risk of LACV infection in high-risk localities, and help in elucidating factors involved in the epidemiology of mosquito-borne arboviruses.